Mass transfer is a physical process that involves diffusive and convective transport of atoms and molecules within physical systems. Mass transfer includes both mixing and separation unit operations. Some common examples of mass transfer processes are the evaporation of water, the diffusion of perfume in air, and the dissolution of sugar in water. Mass transfer is also responsible for the separation of components in an apparatus such as a distillation column.
The driving force for diffusive mass transfer is a difference in chemical potential (or concentration for ideal mixtures); the random motion of molecules causes a net transfer of mass from an area of high chemical potential to an area of low chemical potential. For separation processes, thermodynamics determines the extent of separation, while mass transfer determines the rate at which the separation will occur.
To increase mass-transfer area and/or reduce pressure drop in mass transfer applications, packings can be utilized. In industry, a packed column is a pressure vessel having a packed section. The column can be filled with random dumped packings or structured packing sections, which are arranged or stacked. In the column, liquids tend to wet the surface of the packings and the vapors pass across this wetted surface. Mass transfer takes place across the liquid-vapor interface. In addition, packings can be used to improve separation and/or reduce construction expense and/or provide a lower pressure drop across the column of distillation columns. Differently shaped packings have different surface areas and void space between the packings. Both of these factors affect packing performance.
Existing packings for mass transfer can be divided into random packings and structured packings. Non-limiting examples of random packings include Rashig Rings, Intalox Saddles, Berl Saddles, Pall Rings, and Tellerette; and non-limiting examples of structured packings include corrugated packings, Flexipac, Mellapak, gauzes, grids, and Katapak. Here, random packings have too great of a pressure drop for a given mass transfer area for many applications. Structured packings, while yielding lower pressure drops and often better mass transfer rates than random packings, are expensive to manufacture. In addition, both existing random and structured packings have relatively low surface area to volume ratios.
As such, there is a need for packings that can be easily manufactured while still providing for low pressure drops and high mass transfer rates. In addition, there is a need to have packings with relatively high surface area to volume ratios.